Apparatus for heating rails during the laying down thereof

ABSTRACT

An apparatus for heating railway rails during the laying down thereof, which comprises: a group (1-5) generating a direct current, mounted on a railway car (A); a pair of first contact vices (7) carried by this railway car (A), connected to the output of the generator group (1-5) and suitable for being tightened each one on a first end of the two rails (R) forming the railway track section to be heated; a trolley (B) provided with a similar pair of second contact vices (13), connected to one another and suitable for being tightened on a second end, opposite the first end, of the two rails (R) forming the railway track section to be heated; and means (8-12) for controlling the electric power delivered by the generator group (1-5) in order to produce in the considered railway track section a heating up to a prefixed temperature. Preferably, the group (1-5) generating direct current comprises (1), an alternator (2) moved by the motor (1), a transformer (4) for the current delivered by the alternator (2) and a power rectifier bridge (5) arranged for converting the alternating current coming from the transformer (4) into a direct current to be supplied to the first contact vices (7).

This invention refers to an apparatus for heating railway rails duringthe laying down thereof.

When a long rail section is laid down in conditions of constrainedthermal expansion, according to the presently preferred art, in order toprevent the troubles which, when the temperature of the rail changes,could be caused by an excessive expansion or contraction with respect tothe conditions at the time of laying down, it is needed that thecondition of absence of longitudinal strain (the so-called "null straincondition") in the rail is made to correspond to a prefixed temperaturewhich, for example, for certain railway systems is prescribed to be30°C.±3° C. It would be immediate to obtain this condition if one couldeffect the laying down of the rails and the tightening of the means forfixing the same to the ties when the rail temperature corresponds tothis prefixed temperature but, in general, suitable environmentconditions for doing so are not verified, and the actual temperature oflaying down is lower than the prescribed temperature; therefore,conventionally the so-called "regulation" of the rail is effected, whichcomprises applying to the rail, by means of a mechanical traction, anexpansion calculated in such a manner as to generate in the rail thesame internal strain conditions which would be verified, in the sametemperature conditions, in case the rail would have been laid down atthe prescribed temperature.

According to a manner of operation, which can be deemed the most usualone, when replacing the rails, some rail sections of unitary length,usually in the length of 36 meters as they come from the hot-drawing,are laid down and fixed without welding them, thus forming a railwaytrack which is temporarily used in these poor conditions. At a latertime these rail sections are welded together to form sections separatedfrom the one another by a free joint intended to form the regulationpoint, and the members for fixing the rails to the ties are loosened.Special tensioning clamps are installed in the regulation point, and bymeans of them the facing ends of the sections are drawn the one towardsthe other until the rail section receives an extension calculated as theproduct of the section length multiplied for the thermal expansioncoefficient of the rail and for the difference between the actualtemperature of the rail at the time of the regulation, and theprescribed temperature. At this point, the facing ends of the railsections are welded together and all the members for fixing the rail tothe ties are tightened.

The described operations require interrupting the traffic of the trainson the considered railway track; both the needed operations and the timeduring which the traffic is interrupted give rise to a heavy economical,technical and organization burden, as well as the period during whichthe traffic takes place on the poor railway track formed before theregulation, also involving a certain degree of danger; whereby the railregulation still represents an open problem.

It would therefore be highly desirable that the regulation of the railsforming a railway track could be effected at the same time as theirlaying down, by heating the rails until a temperature higher than theenvironmental one, in order that the tightening of the membersconnecting the rails to the ties could take place at the very prescribedtemperature. To this aim it has been proposed to heat the rails duringtheir laying down by means of free flames, of heating apparatuses actingby irradiation or by electric induction means, but no one of these meansallows obtaining a sufficient evenness in the rail heating along thewhole length of the considered section; moreover, the neededinstallations are too expensive. It has also been proposed, in general,to heat the rails by means of the Joule effect, by having an electriccurrent pass through the rails. However, even if this principle is veryrational in theory, it has turned out that by proceeding, as it appearsobvious, with alternating currents which may be locally generated withease, the skin effect produced by the ferromagnetic character of thematerial forming the rails gives rise to a lack of evenness in thecurrent passing through the cross section of the rails, with theconsequent concentration of the heating in the more superficial regionsof the rails; moreover, the electric voltages needed for proceeding thisway on a railway track of, for example, 144 meters of length, as usual,are not allowable for reasons of safety.

This invention has the aim to solve in a technically rational andeconomically convenient manner the above stated problem, by creating aninstallation for heating railway rails which, by using the knownprinciple of heating the rails by means of the Joule effect, should befree from the stated disadvantages.

This aim is attained, according to the invention, by means of anapparatus which comprises: a group generating a direct current, mountedon a railway car; a pair of first contact vises carried by said railwaycar, connected to the output of said generator group and suitable forbeing tightened each one on a first end of the two rails forming therailway track section to be heated; a trolley provided with a similarpair of second contact vises, connected the one another and suitable forbeing tightened each one to on a second end of the two rails forming therailway track section to be heated, opposite said first end; and meansfor controlling the electric power delivered by said generator group inorder to produce in the considered railway track section a heating up toa prefixed temperature.

Preferably, said group generating direct current comprises a motor, analternator powered by said motor, a transformer for the currentdelivered by said alternator, and a power rectifier bridge arranged forconverting the alternating current coming from said transformer into adirect current to be supplied to said first contact vises.

Preferably said motor is an autonomous Diesel engine or, alternatively,it is the same engine which drives the apparatus, if this latter isprovided with motor means.

Preferably said alternator is of a type having controlled excitation,and some current sensors are inserted between the output of saidrectifier bridge and said first contact vises, some temperature sensorsare applied to an intermediate point of said railway track section, anda process controller is provided for receiving the signals emitted bysaid sensors and for controlling consequently the excitation of saidalternator.

Preferably, said alternator is a three-phase alternator, and it includesa three-phase excitator with an inductor, a polar wheel comprising arectifier bridge and an inductor winding, and three stator windings.

Preferably, moreover, safety control means are connected to said processcontroller in order to interrupt the operation of the apparatus in casecircumstances which are abnormal or capable of causing inconveniences ordanger are verified.

Preferably said contact vises are formed by jaws profiled in a mannercorresponding to the rail section and operated by hydraulic motors.

These and other features, objects and advantages of the subject of thepresent invention will be more clearly apparent from the followingdescription of an embodiment, having the non limitative character of anexample, of an apparatus according to the invention, diagrammaticallyrepresented in the appended drawings, wherein:

FIG. 1 shows a block diagram of the apparatus according to theinvention;

FIGS. 2 to 5 show different steps of the operation of this apparatus;and

FIG. 6 shows the symbols used for distinguishing the various regions ofthe railway track under treatment.

As already said, the use of the Joule effect for heating rails by meansof electric currents passing through them has been already proposed, butthe experiments made in this respect did not give satisfactory results.From the searches and experiments done by the Applicant it has turnedout that these disappointing results were essentially due to the use ofalternating currents. Making use of alternating currents in thisapplication seems to be evident, because the needed energy should begenerated locally by means of generators which, as a rule, include amotor and an alternator. But the alternating current applied to therails, whose constituting material is ferromagnetic, gives rise to anintensive skin effect, whereby practically the current flows only in aregion having a little depth from the external surface of the rail. Onlyin this region the heat is generated, whereby the rail heating can in noway be uniform in its section, and on the other hand the reduced crosssection useful for the current flow gives rise to an increased apparentresistivity of the rail, to which ensues the need of having recourse torelatively high voltages, which cannot be allowed for safety reasons.This is the reason for which the present invention proposes, on thecontrary, to use a direct current, what at first sight could appear as aunnecessary-complication.

Such a direct current may be produced by means of a special generatorincluding a dynamo instead of an alternator, but according to theinvention it is preferable to have recourse to a usual generator whichproduces an alternating current, and then to convert this alternatingcurrent into a direct current, preferably by means of a static powerrectifier bridge.

With reference to FIG. 1, a preferred embodiment of the inventioncomprises, mounted on a railway car A (not shown as such in this Figurebut only in FIGS. 2 to 5, and diagrammatically shown in FIG. 1 by asquare), the component parts shown in said square A. These componentparts include first of all a motor 1 which mechanically drives analternator 2, whose delivered current may be allowed or intercepted bymeans of a switch 3. The motor 1 may be, for example, an autonomousDiesel engine, or, if the railway car carrying the apparatus isself-driving, the motor 1 may be the same motor driving the railway car.In the shown case, the alternator 2 is a three-phase alternator and itincludes a three-phase excitator 2A comprising an inductor 2B, a polarwheel with a rectifier bridge 2D and an inductor winding 2E, and threeinduced stator wind ings 2F.

The switch 3 is followed by a three-phase transformer 4, intended togenerate the relatively low voltage needed for the operation of theapparatus, whereas a power rectifier bridge 5, formed by staticelements, converts the electric current locally generated, which up tothis point was a three-phase alternating current, into a direct current.The delivered current is measured by means of a current sensor 6, thenit is forwarded to a contact group 7 intended to transmit the current tothe rails R forming the railway track section to be heated. To thispurpose, the contact group 7 includes two contact vises 7A and 7B, whichare tightened respectively onto the two rails R of the railway track.Taking into account the high currents to be transmitted, these contactvises are preferably formed by jaws profiled in a manner correspondingto the cross sec- tion of the rails and operated by hydraulic motors.

Moreover, the apparatus according to the invention includes a railwaytrolley 3 (shown as such only in the FIGS. 2 to 5, and diagrammaticallyshown in FIG. 1 by a square), which carries a contact group 13 similarto the already described contact group 7, and comprising two contactvises 13A and 13B similar to the contact vises 7A and 7B, which however,instead of being connected to an electric energy supply, are connectedto one another by a bridge 14.

As it may be understood, when the two contact groups 7 and 13 areconnected to the rails R at the opposite ends of the railway tracksection to be heated, and the apparatus is operated, the currentdelivered through the rectifier 5 passes along a first rail R betweenthe contact vise 7A and the contact vise 13A, the bridge 19 between thecontact vises 13A and 13B, then the second rail R between the contactvise 13B and the contact vise 7B, and it heats these rails R by Jouleeffect. Because the current is direct, the conduction and the heatinguniformly involve the whole cross section of the rails R, thus radicallyavoiding the disadvantages verified in the case of using alternatingcurrents.

One phase of the three-phase voltage generated by the induced statorwindings 2F of the alternator 2 supplies, through a transformer 11 and adiode bridge 12, the inductor winding 2B of the excitator 2A for thealternator 2. Preferably the excitation is controlled by a device 8controlling the alternator excitation, under control of the signalcoming from the current sensor 6 and of a process controller 9 to whichare also sent the signals coming from the temperature sensors 10,suitably applied to the rails R in at least one intermediate point ofthe railway track section to be heated. To the process controller 9 mayalso advantageously be forwarded the signal of an alarm control device15, mounted on the trolley B and having the purpose of interrupting theoperation of the apparatus when any circumstance is verified, that isabnormal or is capable of causing inconveniences or danger. Thereforethe process controller 9, after having compared the rail temperaturevalues given by the sensors 10 with a value imposed by the operator, andonly with the consent of the alarm control device 15, controls theelectric power applied to the rails R by acting on the alternatorexcitation control 8. Thanks to the signal coming from the currentsensor 6, the delivered power may be regulated until the temperatureimposed by the operator is actually obtained, and then maintained, inthe rails R.

In the FIGS. 2 to 5 there are represented different steps of theoperation of apparatus A,B according to the invention, on rails R beinglaid down, this apparatus being synchronized with apparatuses S forwelding the rails and with apparatuses T for arranging the ballast, inview of the fact that in most cases these different operations are to beeffected at the same time. The apparatus according to the invention maybe inserted in a railway line renewal train, between the apparatuses forlaying down the new rails and the apparatuses for welding the same.

The various regions of the line, on which the different operations arecarried out, are identified by special underlying hatches, whosesignificance is clarified by FIG. 6 as follows: D=section where the endstep of the operations is in course; E=section where the step ofarranging the ballast and fixing the rails on the ties is in course;F=section where the rails are being laid down; G =section of railwaytrack where the heating is in course or is foreseen; H=hot railway tracksection; J=last section laid down during the foregoing operation (inmost cases, the day before).

As it may be understood, the operations proceed from left to rightaccording to the Figures.

FIG. 2 shows that when starting the operation it is of advantage to heata railway track section K-L already laid down during the foregoingoperation, in order to attain a uniform regulation at the passage fromthe already laid down rails to the rails being laid down at present.FIG. 3 shows that, when completed the previous heating of the sectionK-L according to FIG. 2 is completed, the apparatuses A,B are advanced(towards the right) for heating a new railway track section L-M (whichin the meantime has been laid down), whilst the welding machine Sadvances for welding the joint L and the ballast arranging machine Tadvances too, behind the welding machine S, for operating on the railwaytrack section already welded and fixed; the operations effected afterthe advancement according to FIG. 3 are represented in FIG. 4. Whenthese operations are completed, a new step of advancement takes placefor heating a further section of railway track M-N, which in themeantime has been laid down (FIG. 5).

An example of the operating conditions of an apparatus according to theinvention will now be set forth, but it should be understood that thebest operating conditions are to be determined for each case by takinginto account the actual rail characteristics and the environmentalconditions. The following example refers to operations effected on railsof the type 60 UNI and on a railway track section of 144 meters.

Cross section of the rail: 7866 square millimeters

Winsor weight: 60 kilograms/meter

Total weight of the section: 17280 kilograms

Specific resistance: 20.82 microohm/meter

Approximate total resistance: 6 milliohm

Desired temperature change: 45 degrees centigrade

Desired duration of the operation: 15 minutes

Approximate power needed: 408 kilowatt

Linear surface of the track section: 0.68 m² /meter

Dispersed power: 246 watts/square meter

Specific dispersed power: 167 watt/meter

Total dispersed power: 50 kilowatt

Total power needed: 460 kilowatt

Current intensity in the track section: 8800 ampere

Maximum voltage at the ends of the section: 52 volt

Minimum gradient of temperature change: 3° C./minute

It will clearly appear to those skilled in the art, when informed by thepresent description about the principles and the characteristics of theinvention, in which manner the operating conditions specified above byway of example should be modified when the starting conditions aredifferent.

The application of this invention allows an effective thermal regulationof the rails laid down during the installation or the renewal of arailway line, by means of relatively quick and cheap operations, whichmay be organized with ease at the time of effecting the other requiredoperations.

Although one embodiment only of the invention has been described, itwill clearly appear to those skilled in the art that this invention mayaccept several changes and replacements by technically equivalent means,without departing from the spirit of the invention and the scope of theappended Claims.

I claim:
 1. Apparatus for simultaneously heating two rails (R) forming atrack section, during the laying down thereof, which comprises: arailway car (A); a generator group (1-5) generating a direct current,mounted on said railway car (A); a pair of first contact vises (7)carried by said railway car (A), connected to an output of saidgenerator group (1-5) and suitable for being tightened one on a firstend of one of said two rails (R) and the other on a first end of theother of said two rails (R) forming the railway track section to beheated; a trolley (B); a pair of second contact vises (13) mounted onsaid trolley (13), connected to one another and suitable for beingtightened one on a second end of one said two rails (R) and the other ona second end of the other of said two rails (R) forming the railwaytrack section to be heated, opposite said first end; and means (8-12)for controlling the electric power delivered by said generator group(1-5) in order to produce in said railway track section to be heated aheating up to a prefixed temperature by passing electric power throughsaid one rail in one direction and simultaneously through said otherrail in an opposite direction.
 2. Apparatus as set forth in claim 1,wherein said group (1-5) generating direct current comprises a motor (1), an alternator (2) powered by said motor (1), a transformer (4) for thecurrent delivered by said alternator (2), and a power rectifier bridge(5) arranged for converting the alternating current coming from saidtransformer (4) into a direct current to be supplied to one of saidfirst contact vises (7).
 3. Apparatus as set forth in claim 2, whereinsaid motor (1) is an autonomous Diesel engine.
 4. Apparatus as set forthin claim 2, wherein further comprises motor means including an enginewhich drives the apparatus, and said motor (1) is the same engine whichdrives the apparatus.
 5. Apparatus as set forth in claim 2, wherein saidalternator (2) is of a type having controlled excitation, and theapparatus comprises some current sensors (6) inserted between the outputof said rectifier bridge (5) and said one of said first contact vises(7), some temperature sensors (10) applied to an intermediate point ofsaid railway track section to be heated, and a process controller (9)arranged for receiving signals emitted by said sensors (6,10) and forcontrolling consequently the excitation of said alternator (2). 6.Apparatus as set forth in claim 2, wherein said alternator (2) is athree-phase alternator, and it includes a three-phase excitor (2A)having an inductor (2B), a polar wheel comprising a rectifier bridge(2D) and an inductor winding (2E), and three stator windings (2F). 7.Apparatus as set forth in claim 5, which includes safety control means(15) connected to said process controller (9) in order to interrupt theoperation of the apparatus in case circumstances which are abnormal orcapable of causing inconveniences or danger are verified.
 8. Apparatusas set forth in claim 1, wherein said contact vises (7,13) comprise jawsprofiled in a manner corresponding to the rail sections (R) andhydraulic motors operating said jaws.